Generally, membranes are used in osmotically driven membrane processes to separate a solvent from solute(s) within a solution. In the case of a forward osmosis (FO) process, a first solution is brought in contact with one surface of the membrane and a second solution is brought into contact with a second, opposing surface of the membrane. Solvent will permeate through the membrane from the less concentrated solution to the more concentrated solution, while the solutes are prevented from passing through the membrane. In the case of reverse osmosis (RO), a solution is brought into contact with one surface of the membrane under pressure. The pressure causes the permeation of the solvent through the membrane, which again prevents the passage of the solutes from within the pressurized solution. Forward and reverse osmosis membranes typically include a thin film barrier layer disposed on a porous support layer.
Traditionally, membrane layers have been manufactured to suit a particular application and via traditional processes. See, for example, U.S. Pat. No. 7,882,963, the disclosure of which is hereby incorporated by reference herein in its entirety. Generally, membranes are put in service, and other than periodic cleaning, perform their intended functions for their useful life. Once a membrane reaches the end of its useful life or otherwise becomes unusable (e.g., damaged), the membrane is replaced and discarded. New membranes are costly and the maintenance/replacement procedures can require a certain amount of system down time, which can be costly and inconvenient. In one case, where the membrane active layer has been damaged, the damage can result in the passage of various solutes through the membrane. Depending on the use of the osmotically driven membrane system, this can result in the loss of valuable solutes (e.g., during concentration of a pharmaceutical product) or passage of toxic substances into a purified product solvent (e.g., during water purification).
There has been much activity recently in the area of incorporating nanoparticles into membranes; however, these efforts have been focused on incorporating the nanoparticles in the initial manufacturing stages to produce a finished membrane. The nanoparticles are typically incorporated into the finished membrane to enhance fouling resistance and improve flux. There does not appear to date to be any effort to repair membranes after manufacture and/or while in use or to modify the performance of existing membranes.